On Fri, 2 Mar 2018 12:34:34 +0000, "J. P. Gilliver (John)"
wrote:

Don't I know it! I have a (possibly similar) elderly friend who doesn't
grasp the concept of folders within folders.


Have you tried asking him to visualize a filing cabinet containing
folders, and several folders in each of them?

Perhaps even better than visualizing it is demonstrating it in an
actual filing cabinet, if you have one handy.